diff --git a/Cargo.lock b/Cargo.lock
index 3c7c254..079ea82 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1810,6 +1810,7 @@ dependencies = [
  "pretty_assertions",
  "rand",
  "reqwest",
+ "retry_future",
  "serde",
  "serde_json",
  "sha2",
@@ -3330,6 +3331,18 @@ dependencies = [
  "tower-service",
 ]
 
+[[package]]
+name = "retry_future"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a831851ed690d7d2ca106ddba947ee9f59e130c00311e815bd6d4ccbefbbc11f"
+dependencies = [
+ "anyhow",
+ "futures",
+ "pin-project",
+ "tokio",
+]
+
 [[package]]
 name = "ring"
 version = "0.17.8"
diff --git a/Cargo.toml b/Cargo.toml
index d94c9d9..546be84 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -113,6 +113,7 @@ codee = "0.2.0"
 
 [dev-dependencies]
 pretty_assertions = "1.4.1"
+retry_future = "0.4.0"
 
 [package.metadata.leptos]
 output-name = "ibis"
diff --git a/migrations/2024-11-11-111150_instances_url/down.sql b/migrations/2024-11-11-111150_instances_url/down.sql
new file mode 100644
index 0000000..fdd4cc0
--- /dev/null
+++ b/migrations/2024-11-11-111150_instances_url/down.sql
@@ -0,0 +1,3 @@
+alter table instance drop column instances_url;
+
+alter table instance alter column articles_url set not null;
diff --git a/migrations/2024-11-11-111150_instances_url/up.sql b/migrations/2024-11-11-111150_instances_url/up.sql
new file mode 100644
index 0000000..7addfa6
--- /dev/null
+++ b/migrations/2024-11-11-111150_instances_url/up.sql
@@ -0,0 +1,3 @@
+alter table instance add column instances_url varchar(255) unique;
+
+alter table instance alter column articles_url drop not null;
diff --git a/src/backend/database/instance.rs b/src/backend/database/instance.rs
index c740e08..1242888 100644
--- a/src/backend/database/instance.rs
+++ b/src/backend/database/instance.rs
@@ -5,7 +5,10 @@ use crate::{
             IbisData,
         },
         error::MyResult,
-        federation::objects::articles_collection::DbArticleCollection,
+        federation::objects::{
+            articles_collection::DbArticleCollection,
+            instance_collection::DbInstanceCollection,
+        },
     },
     common::{DbInstance, DbPerson, InstanceView},
 };
@@ -31,12 +34,13 @@ pub struct DbInstanceForm {
     pub domain: String,
     pub ap_id: ObjectId<DbInstance>,
     pub description: Option<String>,
-    pub articles_url: CollectionId<DbArticleCollection>,
+    pub articles_url: Option<CollectionId<DbArticleCollection>>,
     pub inbox_url: String,
     pub public_key: String,
     pub private_key: Option<String>,
     pub last_refreshed_at: DateTime<Utc>,
     pub local: bool,
+    pub instances_url: Option<CollectionId<DbInstanceCollection>>,
 }
 
 impl DbInstance {
diff --git a/src/backend/database/schema.rs b/src/backend/database/schema.rs
index 7a8e12d..81b43ed 100644
--- a/src/backend/database/schema.rs
+++ b/src/backend/database/schema.rs
@@ -48,13 +48,15 @@ diesel::table! {
         ap_id -> Varchar,
         description -> Nullable<Text>,
         #[max_length = 255]
-        articles_url -> Varchar,
+        articles_url -> Nullable<Varchar>,
         #[max_length = 255]
         inbox_url -> Varchar,
         public_key -> Text,
         private_key -> Nullable<Text>,
         last_refreshed_at -> Timestamptz,
         local -> Bool,
+        #[max_length = 255]
+        instances_url -> Nullable<Varchar>,
     }
 }
 
diff --git a/src/backend/federation/objects/articles_collection.rs b/src/backend/federation/objects/articles_collection.rs
index bc65ec9..94bc273 100644
--- a/src/backend/federation/objects/articles_collection.rs
+++ b/src/backend/federation/objects/articles_collection.rs
@@ -1,14 +1,19 @@
 use crate::{
-    backend::{database::IbisData, error::Error, federation::objects::article::ApubArticle},
-    common::{DbArticle, DbInstance},
+    backend::{
+        database::IbisData,
+        error::{Error, MyResult},
+        federation::objects::article::ApubArticle,
+    },
+    common::{utils::http_protocol_str, DbArticle},
 };
 use activitypub_federation::{
     config::Data,
+    fetch::collection_id::CollectionId,
     kinds::collection::CollectionType,
     protocol::verification::verify_domains_match,
     traits::{Collection, Object},
 };
-use futures::future::{self, join_all};
+use futures::future::{join_all, try_join_all};
 use log::warn;
 use serde::{Deserialize, Serialize};
 use url::Url;
@@ -25,19 +30,26 @@ pub struct ArticleCollection {
 #[derive(Clone, Debug)]
 pub struct DbArticleCollection(());
 
+pub fn local_articles_url(domain: &str) -> MyResult<CollectionId<DbArticleCollection>> {
+    Ok(CollectionId::parse(&format!(
+        "{}://{domain}/all_articles",
+        http_protocol_str()
+    ))?)
+}
+
 #[async_trait::async_trait]
 impl Collection for DbArticleCollection {
-    type Owner = DbInstance;
+    type Owner = ();
     type DataType = IbisData;
     type Kind = ArticleCollection;
     type Error = Error;
 
     async fn read_local(
-        owner: &Self::Owner,
+        _owner: &Self::Owner,
         data: &Data<Self::DataType>,
     ) -> Result<Self::Kind, Self::Error> {
         let local_articles = DbArticle::read_all(Some(true), None, data)?;
-        let articles = future::try_join_all(
+        let articles = try_join_all(
             local_articles
                 .into_iter()
                 .map(|a| a.into_json(data))
@@ -46,7 +58,7 @@ impl Collection for DbArticleCollection {
         .await?;
         let collection = ArticleCollection {
             r#type: Default::default(),
-            id: owner.articles_url.clone().into(),
+            id: local_articles_url(&data.config.federation.domain)?.into(),
             total_items: articles.len() as i32,
             items: articles,
         };
diff --git a/src/backend/federation/objects/instance.rs b/src/backend/federation/objects/instance.rs
index b574d2b..52744c8 100644
--- a/src/backend/federation/objects/instance.rs
+++ b/src/backend/federation/objects/instance.rs
@@ -1,3 +1,4 @@
+use super::instance_collection::DbInstanceCollection;
 use crate::{
     backend::{
         database::{instance::DbInstanceForm, IbisData},
@@ -23,9 +24,10 @@ use url::Url;
 pub struct ApubInstance {
     #[serde(rename = "type")]
     kind: ServiceType,
-    id: ObjectId<DbInstance>,
+    pub id: ObjectId<DbInstance>,
     content: Option<String>,
-    articles: CollectionId<DbArticleCollection>,
+    articles: Option<CollectionId<DbArticleCollection>>,
+    instances: Option<CollectionId<DbInstanceCollection>>,
     inbox: Url,
     public_key: PublicKey,
 }
@@ -86,6 +88,7 @@ impl Object for DbInstance {
             id: self.ap_id.clone(),
             content: self.description.clone(),
             articles: self.articles_url.clone(),
+            instances: self.instances_url.clone(),
             inbox: Url::parse(&self.inbox_url)?,
             public_key: self.public_key(),
         })
@@ -107,6 +110,7 @@ impl Object for DbInstance {
             ap_id: json.id,
             description: json.content,
             articles_url: json.articles,
+            instances_url: json.instances,
             inbox_url: json.inbox.to_string(),
             public_key: json.public_key.public_key_pem,
             private_key: None,
@@ -119,9 +123,17 @@ impl Object for DbInstance {
         let instance_ = instance.clone();
         let data_ = data.reset_request_count();
         tokio::spawn(async move {
-            let res = instance_.articles_url.dereference(&instance_, &data_).await;
-            if let Err(e) = res {
-                tracing::warn!("error in spawn: {e}");
+            if let Some(articles_url) = &instance_.articles_url {
+                let res = articles_url.dereference(&(), &data_).await;
+                if let Err(e) = res {
+                    tracing::warn!("error in spawn: {e}");
+                }
+            }
+            if let Some(instances_url) = &instance_.instances_url {
+                let res = instances_url.dereference(&(), &data_).await;
+                if let Err(e) = res {
+                    tracing::warn!("error in spawn: {e}");
+                }
             }
         });
 
diff --git a/src/backend/federation/objects/instance_collection.rs b/src/backend/federation/objects/instance_collection.rs
new file mode 100644
index 0000000..9670098
--- /dev/null
+++ b/src/backend/federation/objects/instance_collection.rs
@@ -0,0 +1,94 @@
+use super::instance::ApubInstance;
+use crate::{
+    backend::{
+        database::IbisData,
+        error::{Error, MyResult},
+    },
+    common::{utils::http_protocol_str, DbInstance},
+};
+use activitypub_federation::{
+    config::Data,
+    fetch::collection_id::CollectionId,
+    kinds::collection::CollectionType,
+    protocol::verification::verify_domains_match,
+    traits::{Collection, Object},
+};
+use futures::future::{self, join_all};
+use log::warn;
+use serde::{Deserialize, Serialize};
+use url::Url;
+
+#[derive(Clone, Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct InstanceCollection {
+    pub r#type: CollectionType,
+    pub id: Url,
+    pub total_items: i32,
+    pub items: Vec<ApubInstance>,
+}
+
+#[derive(Clone, Debug)]
+pub struct DbInstanceCollection(());
+
+pub fn linked_instances_url(domain: &str) -> MyResult<CollectionId<DbInstanceCollection>> {
+    Ok(CollectionId::parse(&format!(
+        "{}://{domain}/linked_instances",
+        http_protocol_str()
+    ))?)
+}
+
+#[async_trait::async_trait]
+impl Collection for DbInstanceCollection {
+    type Owner = ();
+    type DataType = IbisData;
+    type Kind = InstanceCollection;
+    type Error = Error;
+
+    async fn read_local(
+        _owner: &Self::Owner,
+        data: &Data<Self::DataType>,
+    ) -> Result<Self::Kind, Self::Error> {
+        let instances = DbInstance::read_remote(data)?;
+        let instances = future::try_join_all(
+            instances
+                .into_iter()
+                .map(|i| i.into_json(data))
+                .collect::<Vec<_>>(),
+        )
+        .await?;
+        let collection = InstanceCollection {
+            r#type: Default::default(),
+            id: linked_instances_url(&data.config.federation.domain)?.into(),
+            total_items: instances.len() as i32,
+            items: instances,
+        };
+        Ok(collection)
+    }
+
+    async fn verify(
+        json: &Self::Kind,
+        expected_domain: &Url,
+        _data: &Data<Self::DataType>,
+    ) -> Result<(), Self::Error> {
+        verify_domains_match(&json.id, expected_domain)?;
+        Ok(())
+    }
+
+    async fn from_json(
+        apub: Self::Kind,
+        _owner: &Self::Owner,
+        data: &Data<Self::DataType>,
+    ) -> Result<Self, Self::Error> {
+        join_all(apub.items.into_iter().map(|instance| async {
+            let id = instance.id.clone();
+            let res = DbInstance::from_json(instance, data).await;
+            if let Err(e) = &res {
+                warn!("Failed to synchronize article {id}: {e}");
+            }
+            res
+        }))
+        .await;
+
+        Ok(DbInstanceCollection(()))
+    }
+}
diff --git a/src/backend/federation/objects/mod.rs b/src/backend/federation/objects/mod.rs
index 0b14474..4f83dbf 100644
--- a/src/backend/federation/objects/mod.rs
+++ b/src/backend/federation/objects/mod.rs
@@ -3,4 +3,5 @@ pub mod articles_collection;
 pub mod edit;
 pub mod edits_collection;
 pub mod instance;
+pub mod instance_collection;
 pub mod user;
diff --git a/src/backend/federation/routes.rs b/src/backend/federation/routes.rs
index 5ca4f60..049534c 100644
--- a/src/backend/federation/routes.rs
+++ b/src/backend/federation/routes.rs
@@ -1,3 +1,4 @@
+use super::objects::instance_collection::{DbInstanceCollection, InstanceCollection};
 use crate::{
     backend::{
         database::IbisData,
@@ -47,6 +48,7 @@ pub fn federation_routes() -> Router<()> {
         .route("/", get(http_get_instance))
         .route("/user/:name", get(http_get_person))
         .route("/all_articles", get(http_get_all_articles))
+        .route("/linked_instances", get(http_get_linked_instances))
         .route("/article/:title", get(http_get_article))
         .route("/article/:title/edits", get(http_get_article_edits))
         .route("/inbox", post(http_post_inbox))
@@ -75,8 +77,15 @@ async fn http_get_person(
 async fn http_get_all_articles(
     data: Data<IbisData>,
 ) -> MyResult<FederationJson<WithContext<ArticleCollection>>> {
-    let local_instance = DbInstance::read_local_instance(&data)?;
-    let collection = DbArticleCollection::read_local(&local_instance, &data).await?;
+    let collection = DbArticleCollection::read_local(&(), &data).await?;
+    Ok(FederationJson(WithContext::new_default(collection)))
+}
+
+#[debug_handler]
+async fn http_get_linked_instances(
+    data: Data<IbisData>,
+) -> MyResult<FederationJson<WithContext<InstanceCollection>>> {
+    let collection = DbInstanceCollection::read_local(&(), &data).await?;
     Ok(FederationJson(WithContext::new_default(collection)))
 }
 
diff --git a/src/backend/mod.rs b/src/backend/mod.rs
index 3670053..377af61 100644
--- a/src/backend/mod.rs
+++ b/src/backend/mod.rs
@@ -18,7 +18,7 @@ use crate::{
 };
 use activitypub_federation::{
     config::{Data, FederationConfig, FederationMiddleware},
-    fetch::{collection_id::CollectionId, object_id::ObjectId},
+    fetch::object_id::ObjectId,
     http_signatures::generate_actor_keypair,
 };
 use api::api_routes;
@@ -38,6 +38,10 @@ use diesel::{
     PgConnection,
 };
 use diesel_migrations::{embed_migrations, EmbeddedMigrations, MigrationHarness};
+use federation::objects::{
+    articles_collection::local_articles_url,
+    instance_collection::linked_instances_url,
+};
 use leptos::get_configuration;
 use leptos_axum::{generate_route_list, LeptosRoutes};
 use log::info;
@@ -74,7 +78,8 @@ pub async fn start(config: IbisConfig, override_hostname: Option<SocketAddr>) ->
         .domain(data.config.federation.domain.clone())
         .url_verifier(Box::new(VerifyUrlData(data.config.clone())))
         .app_data(data)
-        .debug(true)
+        .http_fetch_limit(1000)
+        .debug(cfg!(debug_assertions))
         .build()
         .await?;
 
@@ -121,15 +126,14 @@ and to list interesting articles.";
 async fn setup(data: &Data<IbisData>) -> Result<(), Error> {
     let domain = &data.config.federation.domain;
     let ap_id = ObjectId::parse(&format!("{}://{domain}", http_protocol_str()))?;
-    let articles_url =
-        CollectionId::parse(&format!("{}://{domain}/all_articles", http_protocol_str()))?;
     let inbox_url = format!("{}://{domain}/inbox", http_protocol_str());
     let keypair = generate_actor_keypair()?;
     let form = DbInstanceForm {
         domain: domain.to_string(),
         ap_id,
         description: Some("New Ibis instance".to_string()),
-        articles_url,
+        articles_url: Some(local_articles_url(domain)?),
+        instances_url: Some(linked_instances_url(domain)?),
         inbox_url,
         public_key: keypair.public_key,
         private_key: Some(keypair.private_key),
diff --git a/src/common/mod.rs b/src/common/mod.rs
index da8b58e..510baaa 100644
--- a/src/common/mod.rs
+++ b/src/common/mod.rs
@@ -11,6 +11,7 @@ use {
     crate::backend::{
         database::schema::{article, edit, instance, local_user, person},
         federation::objects::articles_collection::DbArticleCollection,
+        federation::objects::instance_collection::DbInstanceCollection,
     },
     activitypub_federation::fetch::{collection_id::CollectionId, object_id::ObjectId},
     diesel::{Identifiable, Queryable, Selectable},
@@ -253,7 +254,7 @@ pub struct DbInstance {
     pub ap_id: String,
     pub description: Option<String>,
     #[cfg(feature = "ssr")]
-    pub articles_url: CollectionId<DbArticleCollection>,
+    pub articles_url: Option<CollectionId<DbArticleCollection>>,
     #[cfg(not(feature = "ssr"))]
     pub articles_url: String,
     pub inbox_url: String,
@@ -264,6 +265,8 @@ pub struct DbInstance {
     #[serde(skip)]
     pub last_refreshed_at: DateTime<Utc>,
     pub local: bool,
+    #[cfg(feature = "ssr")]
+    pub instances_url: Option<CollectionId<DbInstanceCollection>>,
 }
 
 impl DbInstance {
diff --git a/src/database/schema.rs b/src/database/schema.rs
new file mode 100644
index 0000000..81b43ed
--- /dev/null
+++ b/src/database/schema.rs
@@ -0,0 +1,121 @@
+// @generated automatically by Diesel CLI.
+
+diesel::table! {
+    article (id) {
+        id -> Int4,
+        title -> Text,
+        text -> Text,
+        #[max_length = 255]
+        ap_id -> Varchar,
+        instance_id -> Int4,
+        local -> Bool,
+        protected -> Bool,
+    }
+}
+
+diesel::table! {
+    conflict (id) {
+        id -> Int4,
+        hash -> Uuid,
+        diff -> Text,
+        summary -> Text,
+        creator_id -> Int4,
+        article_id -> Int4,
+        previous_version_id -> Uuid,
+    }
+}
+
+diesel::table! {
+    edit (id) {
+        id -> Int4,
+        creator_id -> Int4,
+        hash -> Uuid,
+        #[max_length = 255]
+        ap_id -> Varchar,
+        diff -> Text,
+        summary -> Text,
+        article_id -> Int4,
+        previous_version_id -> Uuid,
+        created -> Timestamptz,
+    }
+}
+
+diesel::table! {
+    instance (id) {
+        id -> Int4,
+        domain -> Text,
+        #[max_length = 255]
+        ap_id -> Varchar,
+        description -> Nullable<Text>,
+        #[max_length = 255]
+        articles_url -> Nullable<Varchar>,
+        #[max_length = 255]
+        inbox_url -> Varchar,
+        public_key -> Text,
+        private_key -> Nullable<Text>,
+        last_refreshed_at -> Timestamptz,
+        local -> Bool,
+        #[max_length = 255]
+        instances_url -> Nullable<Varchar>,
+    }
+}
+
+diesel::table! {
+    instance_follow (id) {
+        id -> Int4,
+        instance_id -> Int4,
+        follower_id -> Int4,
+        pending -> Bool,
+    }
+}
+
+diesel::table! {
+    jwt_secret (id) {
+        id -> Int4,
+        secret -> Varchar,
+    }
+}
+
+diesel::table! {
+    local_user (id) {
+        id -> Int4,
+        password_encrypted -> Text,
+        person_id -> Int4,
+        admin -> Bool,
+    }
+}
+
+diesel::table! {
+    person (id) {
+        id -> Int4,
+        username -> Text,
+        #[max_length = 255]
+        ap_id -> Varchar,
+        #[max_length = 255]
+        inbox_url -> Varchar,
+        public_key -> Text,
+        private_key -> Nullable<Text>,
+        last_refreshed_at -> Timestamptz,
+        local -> Bool,
+    }
+}
+
+diesel::joinable!(article -> instance (instance_id));
+diesel::joinable!(conflict -> article (article_id));
+diesel::joinable!(conflict -> local_user (creator_id));
+diesel::joinable!(edit -> article (article_id));
+diesel::joinable!(edit -> person (creator_id));
+diesel::joinable!(instance_follow -> instance (instance_id));
+diesel::joinable!(instance_follow -> person (follower_id));
+diesel::joinable!(local_user -> person (person_id));
+
+diesel::allow_tables_to_appear_in_same_query!(
+    article,
+    conflict,
+    edit,
+    instance,
+    instance_follow,
+    jwt_secret,
+    local_user,
+    person,
+);
diff --git a/tests/test.rs b/tests/test.rs
index 0a0e08d..fa6606e 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -21,6 +21,7 @@ use ibis::{
     frontend::error::MyResult,
 };
 use pretty_assertions::{assert_eq, assert_ne};
+use retry_future::{LinearRetryStrategy, RetryFuture, RetryPolicy};
 use url::Url;
 
 #[tokio::test]
@@ -673,3 +674,42 @@ async fn test_lock_article() -> MyResult<()> {
 
     data.stop()
 }
+
+#[tokio::test]
+async fn test_synchronize_instances() -> MyResult<()> {
+    let data = TestData::start().await;
+
+    // fetch alpha instance on beta
+    data.beta
+        .resolve_instance(Url::parse(&format!("http://{}", &data.alpha.hostname))?)
+        .await?;
+    let beta_instances = data.beta.list_instances().await?;
+    assert_eq!(1, beta_instances.len());
+
+    // fetch beta instance on gamma
+    data.gamma
+        .resolve_instance(Url::parse(&format!("http://{}", &data.beta.hostname))?)
+        .await?;
+
+    // wait until instance collection is fetched
+    let gamma_instances = RetryFuture::new(
+        || async {
+            let res = data.gamma.list_instances().await;
+            match res {
+                Err(_) => Err(RetryPolicy::<String>::Retry(None)),
+                Ok(i) if i.len() < 2 => Err(RetryPolicy::Retry(None)),
+                Ok(i) => Ok(i),
+            }
+        },
+        LinearRetryStrategy::new(),
+    )
+    .await?;
+
+    // now gamma also knows about alpha
+    assert_eq!(2, gamma_instances.len());
+    assert!(gamma_instances
+        .iter()
+        .any(|i| i.domain == data.alpha.hostname));
+
+    data.stop()
+}